1. Field of the Invention
This invention relates to a light-emitting device employing a semiconductor laser diode as a light source.
2. Description of the Related Art
Conventionally, there have been proposed various kinds of light source devices or light-emitting devices each having a combination of a semiconductor light-emitting element and a fluorescent material (see, for example, JP-A 2008-153617, 2007-158009 and 2006-73202). These light-emitting devices are designed such that an excitation light emitted from a semiconductor light-emitting element is absorbed by a fluorescent material, thereby enabling the fluorescent material to emit a light having a different wavelength from that of the excitation light.
In JP-A 2008-153617, there is proposed a semiconductor light-emitting device which includes a CAN type package and has a combination of a laser diode and a phosphor. Further, in JP-A 2007-158009, there is proposed a thin wall type semiconductor light-emitting device employing a light-emitting diode. Further, in JP-A 2006-73202, there is proposed a light-emitting device for lighting which is equipped with a semiconductor laser element radiating laser beam and with light-guiding plate having a phosphor coated on a light-retrieving face thereof, thereby enabling the light-emitting device to emit light from the surface thereof.
However, in the case of the light-emitting device disclosed in JP-A 2008-153617, although it is made possible to realize a high output because of the employment of a laser diode, the area of emission is circular and wide and there is not provided idea of increasing the luminance. Further, in the case of the light-emitting device disclosed in JP-A 2007-158009, although the light-emitting surface is made narrow to thereby allegedly make it possible to increase the luminance, it fails to create a light-emitting surface which is smaller than the size of the LED element. Further, if it is tried to increase the output of the light-emitting device, the emission area of the LED element per se is required to be increased, resulting in the limitation of any further increase in luminance. Further, in the case of the light-emitting device disclosed in JP-A 2006-73202, although it may be possible to create a linear light source by suitably selecting the configuration of the light-guiding plate, this light-emitting device essentially requires the employment of the light-guiding plate and a cylindrical lens in its structure, resulting in a large number of optical components, thus making the structure complicated and large in size.
Meanwhile, with respect to the installation of the laser diode, in the case of JP-A 2008-153617, the laser diode is fixed to a central portion of the CAN type package. Further, there is also proposed a light-emitting device wherein the laser diode is held inside a heat sink (see, for example, JP-A 2000-150991).
However, in the case of the light-emitting device of JP-A 2008-153617, the control of heat dissipation which requires for increasing the output of laser would become insufficient. Further, in the case of the light-emitting device disclosed in JP-A 2007-158991, although the heat dissipation is ensured by holding the laser diode inside the heat sink, it is impossible to control the spreading of light, thus making it difficult to efficiently utilize the light with the control of only a light source.